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Subject[RFC] [PATCH] [timer] Optimise apply_slack() for size and speed.
Date
To apply proper slack, the original algorithm used to prepare a mask and
then apply the mask to obtain the appropriately rounded-off absolute
time the timer expires.

This patch modifies the masking logic to a bit-shift logic, therby
reducing the complexity and number of operations. Thus obtaining a minor
speed-up.

Signed-off-by: Chinmay V S <chinmay.v.s@pathpartnertech.com>
---
kernel/timer.c | 8 ++------
1 files changed, 2 insertions(+), 6 deletions(-)

diff --git a/kernel/timer.c b/kernel/timer.c
index a297ffc..0379658 100644
--- a/kernel/timer.c
+++ b/kernel/timer.c
@@ -785,9 +785,7 @@ EXPORT_SYMBOL(mod_timer_pending);
* Algorithm:
* 1) calculate the maximum (absolute) time
* 2) calculate the highest bit where the expires and new max are different
- * 3) use this bit to make a mask
- * 4) use the bitmask to round down the maximum time, so that all last
- * bits are zeros
+ * 3) round down the maximum time, so that all the lower bits are zeros
*/
static inline
unsigned long apply_slack(struct timer_list *timer, unsigned long expires)
@@ -811,9 +809,7 @@ unsigned long apply_slack(struct timer_list *timer, unsigned long expires)

bit = find_last_bit(&mask, BITS_PER_LONG);

- mask = (1 << bit) - 1;
-
- expires_limit = expires_limit & ~(mask);
+ expires_limit = (expires_limit >> bit) << bit;

return expires_limit;
}
--
1.7.5.4


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